The present invention relates to an improved work vehicle and more specifically relates to a work vehicle having various improved systems which enhance the performance characteristics of the vehicle and being constructed through improved manufacturing and assembly techniques.
The vehicle disclosed is a lawn and garden tractor which is an example of the smaller range of tractors with which the present invention is particularly adapted for use, such tractors typically including a main frame supported on a rear pair of drive wheels and a front pair of steerable ground wheels, an engine acting through a transmission system for powering the drive wheels and including a power take-off adapted for being connected for driving any powered implements that might be attached to the vehicle, a steering system connected to the steerable front wheels, an operator's station including a seat and a transmission control system for controlling the ground speed of the vehicle.
It is also well known to enclose the tractor engine with a hood and associated baffles or panels in such a way that relatively clean combustion air enters the engine carburetor. Typically, when the engine is water-cooled, the air that flows through the radiator for removing heat therefrom comes from a zone that is different than that from which the combustion air comes. This has the disadvantage of requiring two different screening or filtering assemblies to be provided in order to ensure that the air flowing into the carburetor or through the radiator is relatively free of debris that will adversely affect carburetion or will clog the air passages of the radiator so as to adversely affect cooling of the engine.
Typically, the main frame of such tractors is fabricated from a relatively large number of pieces which are arc welded together. Because the arc welding process involves a substantial input of heat into the metal being welded, relatively heavy material is required in order to minimize material distortion and to make up for strength loss caused by the heat input. Further, the arc welding process has been done mainly by hand resulting in inconsistent welds leading to quality problems.
Heretofore, the most common method of ballasting a tractor properly to accommodate for various front-, mid- or rear-mounted implements has been to mount suitcase weights to the front of the tractor main frame when forward located ballast is desired and to mount wheel weights to the rear wheels when rearward located ballast is desired. Typically, the mounting of the suitcase weights to the main frame has required the mounting of a separate U-shaped bracket to the front of the main frame while wheel weights are somewhat specially made and are cumbersome to mount.
Typically, a tractor is provided with a lift system that is adapted for connection to an implement mounted to the tractor frame for the purpose of raising and lowering the implement between working and transport positions. It is well known to embody helper springs in such lift systems in order to keep the lift effort at a reasonable amount. These helper springs are often adjustable to accommodate for different types of implements having different weights or mounting structure geometries, but some are not easily adjustable and others are not arranged so as to effect a near constant lifting force throughout the range of movement of the particular implement being raised and lowered, as is desirable when the implement is relatively heavy, a rear mounted tiller or a front mounted snowblower being examples of such implements.
The typical tractor steering system includes a gear box having an input shaft coupled for being driven by the tractor steering wheel and an output shaft which is coupled to the steering linkage by a pitman arm. The effective length of the pitman arm determines how much effort must be used in turning the steering wheel in a given situation and determines steering responsiveness, i.e., how many turns lock-to-lock of the steering wheel are required to move the wheels between maximum right-hand and left-hand turning position. Usually, the effective length of the pitman arm is a fixed length chosen as a compromise between that length which would be most desirable for operations where the steerable front wheels are heavily loaded and considerable turning resistance must be overcome, as when a snowblower is mounted to the tractor, for example, and that length which would be most desirable for operations where the tractor must be quickly turned, as when a mower is mounted to the tractor, for example.
The steering systems of many tractors have a fixed steering wheel which may not be properly located for some operators to easily mount or dismount the tractor or for comfortable manipulation by operators of different size. While some tractors have tilt mechanisms for overcoming the above-noted deficiencies, these mechanisms are relatively complex.
Tractors of the type described hereinabove are often equipped with a variable speed hydrostatic transmission including a pump embodying a swash plate that is pivotable, by a speed and direction control lever, to opposite sides of a centered, neutral, zero-displacement position to respective forward and reverse drive positions. It is known to interlock traction drive brake controls with the direction and speed controls of the hydrostatic transmission so that upon the brakes being applied, the control lever is moved to a centered neutral position corresponding to that of the swash plate. However, the structure for interlocking the brake and transmission controls have suffered from one or more of the drawbacks of being too complex or of requiring frequent adjustment in order to ensure that the swash plate is in neutral when the control lever is in neutral.
When a tractor equipped with a hydrostatic transmission of the aforedescribed type is moved without the engine running, the drive wheels act through the drive train coupling them to the output shaft of the motor to drive the motor as a pump. Under these conditions, the fluid in the supply-return lines coupling the pump and motor units together is blocked from flowing freely between the units thus making it very difficult to move the tractor. To overcome this difficulty, it is known to provide a free wheel or bypass valve which is manually actuatable to interconnect the supply-return lines together to thus provide a fluid path which permits the free circulation of fluid between the lines whereby the tractor may be easily moved about. Because it would be harmful to the transmission and/or might provide a safety concern if the tractor engine were started to drive the pump with the bypass valve open, it is known to use a valve which is constantly biased toward its closed position, thus requiring manual effort to be applied during anytime it is desired to move the tractor with the engine not running. Since it is sometimes necessary for the person holding the valve open to simultaneously push and steer the tractor, the task of holding the valve open is sometimes difficult to do.
Lawn and garden tractors of the above-described type are often provided with safety interlock systems embodying an operator presence sensing switch which have the objective of preventing certain operating procedures from being done unless the operator is properly seated on the operator seat. Heretofore, the mountings for the operator presence sensing switches of these systems have suffered from one or more of the drawbacks of being too complex, of requiring constant adjustments and of not working well on slopes.
Thus, it will be appreciated that various aspects of the structure of conventional lawn and garden tractors are in need of improvement.